This invention relates to measurement of the forward and reflected power flow of microwave energy, and especially to a low cost and compact directonal coupler and detector assembly located on waveguide connecting the source and an oven cavity or other load for determining the power flow components.
In order to control the net power flow to a variety of loads in a microwave oven, a power sensor is needed that is adaptable to existing microwave oven designs and which provides output signals related to both the forward and reflected components of wave energy in the waveguide between the magnetron oscillator and oven cavity. A prime requirement is potential low cost and the capability of indicating net power on a continuous basis. The amount of reflected wave energy varies for different food loads and also changes as the food temperature increases, and a good example of the latter is frozen foods because the dielectric properties of ice and water are much different. Having measured the power components, one way of using the information would be to adjust a tuning element to insure minimum reflection at all times and therefore maximum energy transmission with less stress on the magnetron. Other ways to realize improved cooking and oven performance will undoubtedly be suggested.
The directional coupler/detector unit to be described is based on the classical two-hole directional coupler, but the secondary or coupled transmission line system in these is the usual rectangular waveguide. A more compact approach is needed which can be manufactured economically.